Study On Acoustic Cloaking Using Coordinate Transformation

Recently, to control electromagnetic waves and sound waves using coordinate transformation is one of the most popular areas of scientific research. And scientists pay more attention on how to realize cloaking of electromagnetic wave and sound waves. We can use coordinate transformation to get analytical expression of material parameters in a cloak theoretically. With the help of artificial metamaterials, such as split ring resonator, we can adjust the scale of artificial units to achieve proper materials parameters of consistent with theoretical parameters. And then, we can observe the cloaking phenomenon by simulation and experiment. Methods of coordinate transformation and design of artificial metamaterials have a broad potential application, such as cloaking, illusion and acoustic black holes. It will make outstanding contributions to national defense and people’s living.Based on coordinate transformation and long-wave approximation, this letter shows my some research works on the design of acoustic carpet cloak, acoustic illusion, acoustic black holes and so on by using finite element simulation. We also design some models showing how to experimentally realize acoustic carpet cloak. We have done the following work. 1、We have designed acoustic carpet cloak and calculated the material parameters of the cloak. By analysis of acoustic Helmholtz equation with coordinate transformation, we found that due to the form invariant of the propagation equation, only the effect parameters (effect density and effect bulk modulus) will change. Then, we have shown the simulation results of acoustic carpet cloak effects by using the finite element software (COMSOL MUTIPHYSICS).2、We have studied two schemes to realize acoustic carpet cloak in experiment. Firstly, based on transmission line theory, we compared acoustic wave equation and telegraph equation whose forms are the same and got the analogous relationship between acoustic material parameters and inductor-capacitor. We also know that there are some analogous relationships between Helmholtz resonator and IC circuit. So we got the first feasible experimental design to realize the carpet cloaking. Secondly, based on method of long-wave approximation, we have calculated the transmission coefficient and reflection coefficient to retrieve the effect materials parameters (density and bulk modulus) of a unit cell. And then by adjusting the scale of the unit cell we designed another approach to realize acoustic carpet cloak.3、We also have designed several new novel effects using coordinate transmission. Firstly, we have proposed a novel physical concept of simultaneously breaking the parity and time-reversal symmetries in transformation optics, by which nonreciprocal one-way invisible cloak is designed and validated. The one-way invisible cloak is made of a coordinate-transformed nonreciprocal photonic crystal, showing a perfect cloaking for wave incident from one direction but acting as a perfect reflector for wave from the counter direction. The proposed nonreciprocal transformation optics shows a high promise of applications in military, as protecting the own information to be detected but efficiently grabbing the information from the "enemy" side. 4、Secondly, we have also studied the design of an acoustic black hole. The shell of the structure guides the incident acoustic wave into its central cavity spirally without backscattering, thus improving the absorption capacity of the absorptive cavity, which is demonstrated via numerical simulations. Thirdly, based on the concept of complementary media, we have proposed an invisibility cloak operating at a finite frequency that can cloak an object with a pre-specified shape and size within a certain distance outside the shell. Finally, we have also proposed to generate a general acoustic illusion such that an arbitrary object appears to be like some other object that we chose by using coordinate transformation.